I'm in the process of installing on 2012 with the ImageMagickObject as well. When I installed the 64 bit version, I received a nice generic -2147215503 error when trying to run SimpleTest.vbs.

In your case, you may have installed the 32 bit version. The default in windows is to use 64 bit wscript. Try the following from the command line to run the 32 bit version. You'll need to put in your particular version in the path.